Liquid extraction uses relative solubility differences to separate chemical substances from one liquid phase (solvent) into another prior to chemical analysis. Two major types of liquid extraction are Liquid-Liquid Extraction (LLE) and Supported Liquid Extraction (SLE). SLE uses a bed of packing material also referred to as a SLE stationary phase or packing bed. The packing material is placed into a container, such as, a cartridge, column, or well of a 96-well plate.
In one known SLE procedure, an aqueous sample containing analytes is loaded into a SLE container having a packing bed. The packing bed absorbs the sample and spreads it throughout the bed by capillary action. This creates a thin film over the surface area of the packing bed material. To extract analytes of interest, an appropriate organic solvent is introduced into the container to percolate through the packing bed and contact the thin film of aqueous sample. Analytes of interest transfer from the aqueous sample into the organic solvent and are eluted from the container and collected. Water and unextracted impurities remain in the stationary phase. The eluted analytes can then be exchanged into a more suitable solvent for analysis or injected directly depending on the type of detection to be used.
Compared to conventional LLE methods, the SLE approach offers many advantageous features including better reproducibility, lower solvent consumption, elimination or minimization of hazardous solvents, the elimination of emulsions, and is amenable to high-throughput workflows (i.e. automation). The technique of SLE has been widely applied in pharmaceutical industries, forensic chemistry, and environmental analysis.
The success of SLE extraction relies on the quality of the stationary phase materials. Ideally the stationary phase should provide a consistent flow pattern, high cleanliness, comparable or better performance as LLE, and low cost. Conventionally, the packing material used in SLE devices is diatomaceous earth, which is a naturally occurring material composed mostly of silica. Although diatomaceous earth is cost-effective it suffers from a series of issues including lot-to-lot variation in particle morphology, shape and unwanted impurities. Additionally, low levels of crystalline silicon dioxide incurred in diatomaceous earth may present occupational health risks to workers' including silicosis and carcinogenicity necessitating strict regulatory controls in manufacturing environments. There is a need for alternative packing materials for SLE methods that can provide superior material consistency, cleanliness, cost effectiveness, and with less health concerns.
A synthetic sorbent different from the present disclosure has been made available by Phenomenex (Torrance, Calif.) currently referred to as a SLE product, Novum™. Unlike conventional SLE products based on diatomaceous earth, the Novum™ product appears to use a synthetic SLE sorbent for both SLE tubes and 96 well plates.